This invention relates in general to the construction and operation of plasticizing devices and, in particular, to a new and useful process and apparatus for the manufacture of molded parts from granulated plastics wherein the granular plastic material is fed into a vertically elongated vestibule through which hot gases are circulated upwardly through the plastic materials or after wetting the granular material with a reactive monomeric preproduct, it is subjected to a surface polymerization and subsequently the plastic pile becomes weldable and it is abruptly pressed into the mold cavity using a movable ram.